1. Field of the Invention
The present invention relates generally to a motion initiator for a shaft or other object, and, more particularly, to such an initiator which is non-explosive and operates on the electrical destruction of a link wire element.
2. Description of Related Art
There are many situations (e.g. fire fighting systems) which require the initiation of motion of an object or shaft on demand in a precisely timed manner and with high reliability. One approach to solving this problem has been to restrain a spring-loaded member desired to be moved and explosive means are detonated to sever or rupture the restraining means, thereby achieving rapidly timed and precise movement of the member by the spring action. The use of explosive means, however, is not applicable to a wide range of applications in view of the possibility of danger or destruction to surrounding equipment and personnel.
In copending U.S. patent application Ser. No. 08/226,704 filed Apr. 12, 1994, MOTION INITIATOR, by Larry L. McCormick, a pair of substantially semi-cylindrical spool halves are fitted together in a releasable manner along with an insulative body located between the two spool halves to surroundingly secure and restrain a body which is subjected to a force urging movement. A retaining wire is helically wound around the spool halves and ceramic body securing these pieces together in a unitary relationship, one end portion of the retaining wire being held by a link wire anchored in the insulating body and preventing the retaining wire from unwinding to release the spool halves. On electrical actuation a current passes through the link wire causing it to experience breakage, the current causing the tensile strength of the link wire to reduce to such a point that tensile load placed on it by the retaining wire breaks it. In this manner the spool halves and included object or shaft are released enabling its movement. The described prior art initiator is not fully satisfactory in that the link wire found best for this use is of stainless steel construction and has a very small cross-section (e.g., 0.004 inches) which makes it difficult to terminate both electrically and mechanically. For example, effecting electrical connection to the link wire is difficult since due to the wire small cross-section, the heat mass is accordingly small and the wire can be damaged by soldering or other application of heat. Also, despite the small size of the wire, it must still be able to withstand the tensile force exerted by the retaining wire coil which is continuously exerted upon it and which may be exerted upon the link wire for a long period of time. Moreover, to bend or kink the link wire during termination or assembly can result in a weak point that may rupture prematurely.